1. Field of the Invention
The present invention relates to the field of manufacturing organic electroluminescent display devices, and more particularly to a cleaning method and a cleaning apparatus for a mask.
2. Discussion of the Related Art
LCDs are characterized by attributes such as thinner, power-saving, and low radiation, and thus have been greatly adopted in mobile phones, digital cameras, computers, and TV panels. Currently, most of the LCDs are backlight type, which includes a liquid crystal panel and a backlight module opposite to the liquid crystal panel. The backlight module provides a display light source to the liquid crystal panel such that the liquid crystal panel may display images. With the development of the technology, users demand toward high performance of liquid crystal panel have been increased. In order to enhance the color saturation, the chromaticity of the display images may be improve by enhancing the chromaticity of the light bars within the backlight module. Currently, the chromaticity may be enhanced by adopting quantum dots (QD) technology.
QD may also be called as nano-crystal, which is composited by a limited number of atoms whose size in three dimensions is completely within the nanoscale. Usually, the QD may be manufactured by semiconductor materials, such as elements of Group II-VI group or Group III-V, and the diameter of the nano-particle may be in a range of 1 and 10 nm. The QD is complex of atoms and molecules within the nanoscale. The QD may include one semiconductor group, such as Groups II and VI (CdS, CdSe, CdTe, and ZnSe), or Groups III and V (InP and InAs). In addition, the QD may include two or more than two semiconductor groups. QD is of the semiconductor nano-structure binding the conduction band electrons, the holes in the valence band, and exciton in three dimensions. As the conduction band electrons and the holes in the valence band are limited by quantum, the continuous energy band structure converts into discrete energy structure, which may emit fluorescent lights after being activated. QD may be applied into lighting and display fields by changing the attributes of the wavelength of the incident lights via the crystals having different sizes. Thus, the color may be precisely controlled by configuring the sizes of the crystals.
Full width at half maximum (FWHM) of QD is usually small, such as in a range of 20 nm and 50 nm, and thus is feasible for backlight. With respect to the LCDs having QD fluorescent powder backlight, the color range may be better than the LCDs having YAG fluorescent backlight for at least 50%. Thus, such LCDs may be more vivid and the stereoscopic performance is better.
Currently, QD fluorescent powder may be applied to the LED light source. Mainly, after the LED chip is encapsulated, the QD fluorescent powder and silica gel are mixed and then are coated on a light emission surface of the LED chip to form a QD fluorescent powder film. The QD fluorescent powder may be invalidated due to oxidation, and quenching effects with respect to the temperature is serious. With the temperature increment, the light emitting efficiency drops seriously. Thus, the above technical solution lacks the protection toward the QD fluorescent powder. This not only reduces the life cycle of the QD fluorescent powder, but also deteriorates the light emitting efficiency and uniformity of the light color.